326 



FOURTH GROUP. — SEED-PLANTS. 



of resemblance to other microspores and especially to those of the Marsiliaceae, in 

 which the swelling endosporium protrudes in the same way out of the exosporium. 



The structure of the female flowers varies much in the different divisions of the 

 Coniferae; the position of the ovules (macrosporangia) is especially variable, and 

 resembles in this respect the position of the sporangia in Vascular Cryptogams. In 

 Taxus the macrosporangia terminate a small leafy axis ; in Gingko they are placed 

 more than one together on a peculiar branch ; in the Cupressineae on a projection 

 in the axil of a scale-leaf; in most other species immediately upon a leaf, or on a 



riG. 254. Abies pectiiiala. ^ a male flower ;* delicate 

 bud-scales forming a sort of perianth, a the stamens. B a 

 pollen-grain ; e its exine which forms the two large bladdery 

 swellings */. B after Schacht. 



Fig. 255. A pollen of Thuja on'enfah's before pollina- 

 tion ; / fresh, //, /// after lying in water, in which case 

 the exine e is stripped off by the swelling of the intine ;'; 

 /! space left beneath the intine. B pollen o{ Punts Pinaster 

 before the bursting of the pollen-sac ; e the exine with its 

 bladder-like swellings bl, magn. 550 times. 



placenta formed on a leaf and often of very peculiar construction. In Taxus, for 

 example, each macrosporangium is a female flower ; in other genera, as Pmus, the 

 female flowers have the well-known cone-form, and consist of a number of scale-leaves 

 which bear one or more macrosporangia on their upper or dorsal surface. 



The simplest forms of female flowers are to be found in the Araucarieae, and 

 these are closely allied to the male ' catkins ' above described and to analogous 

 structures in most of the Vascular Cryptogams. But while the microsporangia 

 (pollen-sacs) are on the under side of the sporophyll (staminal leaf), the macro- 

 sporangia are inserted on the upper side of the leaf that bears them. The genus 

 Dammara presents the simplest case (Fig. 256, i, 2). The scales of the cone bear on 

 their upper side a macrosporangium with an integument (Fig. 256, 2 Jnt), which 

 shows one or two wing- like expansions (Fig. 256, i, 2 fl). The micropyle is turned 

 towards the axis of the cone (Fig. 256 Mi). The macrosporangium is formed 

 originally, according to Dickson ^, close to the base of the scale and carried further 

 upwards by the intercalary growth of the basal portion. The arrangement is quite 

 similar in the genus Araucaria, only there the part of the integument which is turned 

 towards the scale is not free, and therefore the macrosporangium is only co\ered 

 by an integument on its outer side (Fig. 256, 3). In this case there is an out- 

 growth from the scale of the cone above the macrosporangium (Fig. 256 /), which in 



Transactions of the Botan. Soc. of Edinburgh, 1S61. 



